This invention relates to an improved disc separator and more particularly, to an improved disc assembly within the separator and to a method of making such a disc assembly.
Disc separators are used in wood products and other industries for screening large flows of material such as wood chips to separate larger chunks of material from finer pieces. A separator usually comprises a plurality of disc assemblies mounted in parallel for rotation in the same direction to form a moving screen. Each disc assembly includes a hub and a row of parallel discs mounted thereon. The discs of adjoining assemblies interleave with a narrow spacing that permits only the finer material to pass through the slots between the discs. The larger chips screened out are carried by the rotating discs to the discharge end of the screen.
A long-standing problem with disc separators has been the difficulty of maintaining uniformity of spacing between the discs. Slot widths between overlapping discs may be as little as 1/5 inch. Even a slight misalignment of a disc from the parallel can vary the slot width arbitrarily and allow unacceptable chips through the screen. Furthermore, the misalignment can also cause overlapping discs to rub against each other and quickly wear out.
Heretofore, the discs have been secured to a hub by a number of different methods. In U.S. Pat. No. 4,037,723 to Wahl et al. and in my own U.S. Pat. No. 4,239,119, the discs are splined onto the hub and spaced apart in parallel by intervening spacers. Although the discs may be uniformly spaced using this approach, they are not securely fastened to the hub at their bases to prevent the discs from wobbling. The only force holding the discs in alignment is compression from plates on the ends of the hub. Moreover, the planar surface of the disc has little rigidity and bends when pressured by large wood chips that can wedge between overlapping discs.
An alternative method for fastening discs to the hub is disclosed in U.S. Pat. No. 4,301,930 to Smith. Rather than relying on spacers or spline slots to align the discs closely to one another, the discs are welded at their bases directly to the hub. The welding, however, does not provide any further rigidity to the disc surface. Furthermore, welding the disc directly to the hub has its own drawbacks. It introduces thermal stresses to the metal of a disc that can warp the planar surface and thus cause the spacing between discs to vary.
Therefore, a need remains for a disc assembly having the discs securely mounted to the hub for proper alignment and for a method of making such a disc assembly.